Fluid pressure brake



Marbh 23, 1937. P, S 6 2,074,761

FLUID PRESSURE BRAKE Filed Aug. 1, 1956 INVENTOR EVERETT P. SEXTIJN{ATTORNEY Patented Mar. 23, 1937 UNITED STATES PATENT FLUID PRESSUREBRAKE Application August 1,

12 Claims.

This invention relates to fluid pressure brakes and more particularly tothe type adapted to operatc upon a reduction in brake pipe pressure toeffect an application of the brakes and upon an increase in brake pipepressure to effect a release of the brakes.

In Patent-2,031,213, issued to Clyde C. Farmer on February 18, 1936,there is disclosed a fluid pressure brake equipment including a servicevalve device which is operative upon a service reduction in brake pipepressure to effect a service application of the brakes, and an emergencyvalve device which is operative along with the service valve device uponan emergency reduction in brake pipe pressure to effect an emergencyapplication of the brakes.

In the emergency valve device, a piston is provided which is subject tothe opposing pressures of the brake pipe and a valve chamber. The valvechamber is in communication with a quick action chamber through arelatively large passage through which the pressures in said valve andquick action chambers are adapted to vary substantially together. Thepiston is adapted to be operated by the pressure of fluid in the valveand quick action chambers upon a service rate of reduction in brake pipepressure to move an auxiliary slide valve to a service position in whichfluid under pressure is vented from said 3 chambers at such a rate as toprevent a sufficient differential of pressures being developed on saidpiston upon a service reduction in brake pipe pressure as to cause saidpiston to move said valve past the service position to an emergencyposition in which an emergency application of the brakes would beeffected. The emergency piston and auxiliary slide valve are soproportioned as to be moved to service position by a relatively smalldifferential, such as .4 of a pound,

between the pressures in the brake pipe and quick action chamber. Inorder to stabilize this service action of the piston against possibleundesired movement past the service position as. would tend to occurbefore the pressure in the valve and quick action chambers had time toreduce any appreciable degree, a spring is provided to become effectivesubstantially in service position to oppose further movement of thepiston. This spring is of such value as to require a definite increase,such as .5 of a pound, in the differential of pressures on the emergencypiston to cause same to move past service position, so it, therefore, tostop said piston in the service position in which the venting of fluidfrom the,

1936, Serial No. 93,780

valve and quick action chambers will prevent obtaining said increase indifferential.

The communication through which fluid under pressure is vented from theemergency valve and quick action chambers in service position of the 5auxiliary slide valve is restricted to such a de-- gree that thepressure therein can not reduce as fast as the brake pipe pressurereduces upon an emergency reduction in brake pipe pressure in which casethe difierential of pressures on the emergency piston will promptlyincrease, even in service position, to a degree such as one pound, whichis normally sufiicient to overcome the pressure of the spring acting onthe piston and then move the auxiliary slide valve to the emergencyposition for initiating an emergency application of the brakes.

It has been found that the static resistance to movement of theemergency piston occasionally increases due, it is believed, to slightdeposits of foreign matter on and around the piston and on the pistoncylinder wall and this foreign matter tends to prevent the piston fromstarting to move on the differential of pressures intended. If thisstatic resistance to movement of the piston becomes sufficiently great,there is a possibility that such a high differential of pressures willbe obtained on said piston before it starts to move that after it startsto move upon a service reduction in brake pipe pressure, its inertia and0 the rapidity of its movement will be such that the restricted serviceventing of fluid under pressure from the valve and quick action chambersand the pressure of the spring which comes into action in the serviceposition will not be sufiicient to stop said piston in service position,and as a result, said piston will move on to emergency position andthereby initiate an undesired emergency application of the brakes.

This undesired movement of the emergency piston to emergency positionupon a service recluction in brake pipe pressure is dependent upon asufficient differential of pressures being maintained on said piston asit moves, to keep it going, and such may occur since the relativelylarge communication connecting the quick action chamber to the valvechamber permits the pressure in the valve chamber to be maintainedsubstantially equal to that in the quick action chamber, regardless ofhow fast the emergency piston moves away from its normal position andregardless of the fact that such movement increases the volume of thevalve chamber by an amount equal to the displacement volume of saidpiston as it moves.

It is undesirable to have an emergency application of the brakes occurupon effecting a service reduction in brake pipe pressure since suchgenerally results in the stopping of a train which interferes with theoperating schedule thereof. Further, an emergency application of thebrakes is liable to cause damage to the cars in a train or to the ladingcarried thereby, and the principal object of the invention is to provideimproved means for preventing an emergency application of the brakesfrom occurring upon a service reduction in brake pipe pressure due toconditions such as above described.

Other objects and advantages will be apparent from the following, moredetailed description of the invention.

In the accompanying drawing, the single figure is a diagrammatic view ofa portion of a fluid pressure brake equipment embodying the invention.

The portion of a fluid pressure brake equipment, shown in the drawing,is similar to a corresponding emergency portion of the brake equipmentdisclosed in the aforementioned patent, but only those parts are shownwhich are deemed essential to a comprehensive understanding of theinvention.

The portion of a fluid pressure brake equipment, shown in the drawing,comprises a pipe bracket I having a face upon which there is mounted anemergency valve device 2 and a brake pipe vent valve device 3. Connectedto the pipe bracket is a brake pipe 4, an emergency reservoir 5 and abrake cylinder 6.

The emergency valve device 2 comprises an emergency piston I, having atone side a chamber 8 connected to the brake pipe 4 through passages 9and I0, and having at the opposite side a valve chamber I I which isconnected to a quick action chamber or volume reservoir I2 through apassage I3.

A main slide valve I5 and an auxiliary slide valve I6 are disposed inthe valve chamber II for operation by the piston I through the medium ofa stem I! carried by said piston. The stem H has a cavity in which theauxiliary slide valve I6 is disposed and is provided with spacedshoulders I8 and I9 adapted to engage the main slide valve I5 for movingsame. The outer end of the piston stem I1 is slidably mounted in asuitable bore in the casing of the device and carries a plunger 20movable longitudinally of the stem in alignment for engagement with theleft hand end of the main slide valve I5. A spring 2| in the stem IIacts on the plunger 20 urging same to its normal position which isslightly to the right of the shoulder I9 on the stem, as shown in thedrawing.

The brake pipe vent valve device comprises a vent valve 23 contained ina chamber 24 which is connected to brake pipe 4 through passages 25, 26,9 and II], and further comprises a piston 21 which is operative tounseat said vent valve through the medium of a connecting stem 28. Aspring 29 in chamber 24 acts on the vent valve 23 normally urging sameto its seated position for closing communication from chamber 24 to achamber 30 which is open to the atmosphere.

In operation, in order to initially charge the equipment with fluidunder pressure, fluid under pressure supplied to brake pipe 4 in theusual well known manner flows therefrom through passages I6 and 9 to theemergency piston chamber 8 and also from passage 9 through passages 26and 25 to the vent valve chamber 24.

With the parts of the emergency valve device in their normal position,as shown in the drawing, fluid under pressure supplied to chamber 8flows through a restricted charging port 3| to passage I3 and fromthence in one direction to the emergency valve chamber II and in theopposite direction to the quick action chamber I2.

In charging the equipment with fluid under pressure, the service portionof the equipment (not shown) is operated to supply fluid under pressureto passage 32 and from thence to the emergency reservoir 5 for chargingsaid reservoir and is also operated to open the brake cylinder 6 to theatmosphere so as to provide for a release of brakes, but theseoperations do not enter into the invention and a more completedescription thereof is, therefore, not deemed essential.

In order to effect a service application of the brakes, a service rateof reduction is effected in the pressure in brake pipe 4 andconsequently in the pressure in the emergency piston chamber 8 and fluidunder pressure then tends to flow back from the valve chamber II andquick action chamber I2 to piston chamber 8 through the restrictedcharging port 3|, but this flow back of fluid under pressure is sorestricted that the brake pipe pressure promptly starts reducing belowthe pressure acting in the valve chamber II.

If the static resistance to movement of the emergency piston I issubstantially normal, then when the brake pipe pressure acting inchamber 8 is reduced slightly, such as .4 of a pound, below the pressurein the valve chamber II, the differential of pressures acting on saidpiston moves same and thereby the auxiliary slide valve I6 towards theright hand relative to the main slide valve I5 causing the service port32 in said auxiliary slide valve to move into registry with the serviceport 33 in said main slide valve, and through these ports and anatmospheric passage 34 fluid under pressure is vented from the valvechamber II and quick action chamber I2 to the atmosphere at such a rateas to reduce the pressure in said chambers at substantially the samerate as the brake pipe pressure in chamber 8 is reduced, so as tothereby reduce the differential of pressures on said piston to preventsaid piston from moving the auxiliary slide valve I6 past serviceposition.

At about the time that the port 32 moves into full registry with port33, the plunger 20 engages the left hand end of the main slide valve I5so that further movement of said piston towards the right hand isopposed by the pressure of spring 2| acting on said plunger, whichspring is of such value as to require a predetermined increase, such as.5 of a pound, in the differential of pressures acting on piston I inorder that said piston I may continue its movement towards the righthand. This spring, therefore, acts to stabilize the piston againstmoving the auxiliary slide valve I6 past the service position, to thatthe vent communication through ports 32 and 33 and passage 34 willfunction to reduce the pressure in chambers II and I2 in the mannerabove described.

If an emergency rate of reduction in pressure is effected in the brakepipe 4 and consequently in piston chamber 8, a differential of pressuresis promptly established on the emergency piston I as hereinbeforedescribed, and if the emer- L corresponding reduction is effected in thepresgency valve device is in proper working condition, the piston Ipromptly moves the auxiliary slide valve I6 to the service position inwhich port 32 registers with port 33. The venting capacity of theseports is, however, so restricted that the pressure in chambers II and I2can only reduce at a service rate which is slower than an emergency rateof reduction in brake pipe pressure. As a consequence, the differentialof pressures on the emergency piston 'I promptly increases to a Valuewhich overcomes spring 2I and moves said piston and thereby theauxiliary slide valve I6 to emergency position which is defined by theengagement of shoulder I3 on the piston stem I! with the left hand endof the main slide valve I5.

In this emergency position, the auxiliary slide valve I6 uncovers anemergency port 35 which permits fluid under pressure to flow from thevalve chamber II and quick action chamber I2 through said port topassage 36 and from thence to chamber 31 at the left hand side of thevent valve piston 21. The pressure of fluid thus obtained on the ventvalve piston 21 shifts said piston in a direction towards the right handand thus unseats the vent valve 23 against the pposing pressure ofspring 29.

When the vent valve 23 is unseated, fluid under pressure is suddenlyvented from the brake pipe 4 through passages II], 9, 26 and 25, throughchamber 24 to chamber 30 and from thence to the atmosphere, this suddenreduction in brake pipe pressure being effected to cause the emergencyvalve device on the next car in a train to operate in a similar mannerand thus transmit emergency operation serially from car to car through atrain.

When the brake pipe pressure is suddenly reduced by the operation of thevent valve 23, a

sure in the emergency piston chamber 8 and this promptly provides asufiicient differential of pressures on the emergency piston I to causesame to shift the main slide valve l towards the F right hand to aposition in which said piston seals against a gasket 38.

In this position of the emergency piston I and slide valve I5 said slidevalve uncovers passage 33 so that fluid under pressure then flowsdirectly from chambers II and I2 to said passage and from thence tochamber 31 so as to maintain the vent valve 23 unseated to ensurecomplete venting of fluid under pressure from the brake pipe 4. In thisposition of the slide valve 15, a cavity 39 therein connects a passage40,

which is connected to the emergency reservoir 5, to a passage 4| leadingto the brake cylinder 6 and through this communication fluid underpressure is permitted to flow to said brake cylinder for effecting anemergency application of the brakes.

If the static frictional resistance to movement of the emergency pistonI becomes increased due to accumulation of foreign matter or the like onthe piston or on the wall of the cylinder in which the piston operates,it will be evident that said piston will not move the auxiliary slidevalve I6 to service position when a .4 pound differential of pressuresis obtained on said piston upon a service reduction in brake pipepressure, as hereinbefore described. Instead, the differential ofpressures must be increased to a degree sufficient to overcome thestatic resistance to movement of the piston, and if said staticresistance and differential become sufficiently great before the pistonstarts moving, then after the piston does start, the differential willtend to move said piston and auxiliary slide valve I6 so fast and withsuch force that said piston will tend to quickly overcome the pressureof spring 2i and move through service position to emergency position andthereby initiate an emergency application of the brakes, which isundesired upon a service reduction in brake pipe pressure.

According to the invention, a choke or restriction I4 is provided in thepassage I3 between the quick action chamber I2 and valve chamber II inorder to prevent such an undesired emergency application of the brakesoccurring upon a service reduction in brake pipe pressure.

The choke I4 is provided to restrict the flow of fluid under pressurefrom the quick action chamber I2 to thevalve chamber II to such a degreethat the pressure in said valve chamber will not be maintained from saidquick action chamber, when, after a high differential of pressures isdeveloped on said piston due to its being stuck by foreign matter or thelike, it suddenly lets go and in effect, jumps towards service andemergency positions. In other words, when the emergency piston I movestowards the right hand it in effect increases the volume of the valvechamber I I at the left hand side of said piston an amount equal to thedisplacement volume of the piston, and due to the action of choke I4 tohold back the flow of fluid under pressure from quick action chamber I2to the valve chamber II and the rapidity of the movement of said pistonunder such conditions, a very material reduction in pressure occurs inthe valve chamber I I which will reduce the differential on said pistonto a degree where it will stop moving before emergency position isreached, at which time the service ports 32 and 33 are in registry,venting fluid under pressure from said valve chamber II, and the spring2! is also efiective, so that once said piston is stopped orsubstantially so, the venting action of the service ports 32 and 33 andthe action of spring M will prevent suflicient differential from beingagain obtained on said piston to cause it to again start moving upon theservice reduction in brake pipe pressure.

To be more specific, the actual volume of the valve chamber II, i. e.,the chamber at the left hand side of the emergency piston I, when saidpiston is in its normal position, is about cu. in, while the volume ofthe quick action chamber I2 is about 160 cu. in., making a total volumeof 1'20 cu. in.-normally charged with fluid under pressure for movingthe emergency piston 'I and slide valves I5 and I6 upon a reduction inbrake pipe pressure.

The piston 'I is substantially 10 sq. in. in area and its movement andthat of the auxiliary slide valve I6 from normal position to serviceposition, in which the ports 32 and 33 are in full registry, is about.096 in. This movement of the piston I will, therefore, increase thevolume of the valve chamber I I about .9 cu. in. With the passage I3sufficiently large to permit the large volume of fluid under pressure inchamber I2 to substantially maintain the pressure in valve chamber I Iequal to that in chamber I2 upon sudden movement of piston I, thereduction in pressure in said chamber, due to its increase in volume by.9 cu. in., on account of the displacement of said piston, will have nomaterial effect upon stopping the piston from moving on to emergencyposition upon a service reduction in brake'pipe'pressure. In otherwords, assume that the static resistance of said piston is such as torequire a three pound differential-to start it moving. A reduction inthis differential to 2.55 pounds, due to the displacement volume of thepiston after it starts moving, will not stop said piston from movingonto emergency position. The relatively low kinetic friction of the partsalso aids in permitting the slightly reduced differ ential of fluidpressures to efiect such movement to emergency position.

The choke [4, however, acts to retard the flow of fluid under pressurefrom the quick action chamber l2 to the valve chamber ll upon suddenmovement of the emergency piston I, as just described, so that when saidpiston suddenly moves from its normal position, the displacement volumethereof will effect suflicient reduction in pressure in the valvechamber II to reduce the diiferential of fluid pressures on said pistonto a very low degree or substantially zero, depending upon the rapidityof movement of the piston after it breaks loose, and this reduction indifferential will cause said piston to stop.

To be more specific, if the volume of valve chamber H is suddenlyincreased from 10 cu. in. to 10.9 cu. in. by movement of the piston fromits normal position to, say, service position, the action of choke Mwill permit reduction in pressure in said valve chamber of around fivepounds from seventy pounds, such as normally carried in freight service.Such a reduction in pressure in valve chamber II is sufficient tobalance the pressures on the emergency piston and cause it to ceasemoving even if such an excessive reduction as five pounds in brake pipepressure were required to break it loose. If the piston only requiredthree pounds difierential to start it moving, obviously the pressures onthe piston could be substantially balanced and the piston therebystopped before the service position were reached. The auxiliary slidevalve I6 may move .020 inch past the service position, in which ports 32and 33 are in full registry, before the emergency port 35 starts toopen, and during which movement the service ports 32 and 33 are still inpartial registry, so it will be evident that even if in a remoteinstance an emergency piston should require a differential such as sixor seven pounds to start it moving, this further movement of theemergency piston is capable of providing sufficient reduction inpressure in the valve chamber to stop the piston.

After the emergency piston l is once moved out of its normal positionand then stopped before the emergency position is reached, the serviceports 32 and 33 will be in registry to permit the venting of fluid underpressure from valve chamber II and quick action chamber in the samemanner as hereinbefore described.

The choke I4 is operative to prevent undesired movement of the emergencypiston to emergency position, as above described, only upon a servicerate or reduction in brake pipe pressure; it cannot prevent movement toemergency position upon an emergency rate of reduction in brake pipepressure and will not have any material effect upon such intendedoperation.

The fact that the choke M will accomplish the purpose intended is due tothe fact that a service rate of reduction in brake pipe pressure isrelatively slow, and if, for instance, a three pound differential ofpressures is required on the emergency piston to start it moving, thebrake pipe pressure is only reduced to sixty-seven pounds, assumingseventy pounds pressure to be that normally carried, at the instant saidpiston breaks loose and starts moving, and the movement is so rapid,that the pressure in the valve chamber need only be reduced to that inthe brake pipe at that instant, or substantially sixty-seven pounds, tostop movement of said piston.

Upon an emergency rate of reduction in brake pipe pressure however, theaction of choke I4 will not prevent the intended movement of theemergency piston to emergency position, because the brake pipe pressurereduces so rapidly that, before the piston can be stopped ahead of theemergency position, suflicient differential is obtained thereon tocontinue its movement to the emergency position, and this continuedmovement is also aided by the relatively low kinetic friction of themoving parts at this time.

It will be apparent that the choke 14 has relatively large flow capacityas compared, for instance, to that of the restricted charging port 3|and will have no effect upon operation of the emergency valve deviceupon a service reduction in brake pipe pressure, if the piston I is incondition to operate as intended.

The particular location of the choke M in the passage I 3 is notpertinent since its only function is to retard the flow of fluid underpressure from the quick action chamber I2 to the valve chamber II.

It will be further understood that the drawing is merely diagrammatic toillustrate the use of the invention and is not intended to showdimensions and volumes of such size or proportions mentioned in theabove description of the invention.

From the above description of the invention, it will be evident that avery simple, but novel means, has been provided adapted to be employedin connection with emergency valve devices such as above describedwhereby undesired emergency operation thereof may be prevented upon aservice reduction in brake pipe pressure, in case the static resistanceto movement of the emergency piston becomes increased to a degreegreater than normal, due to accumulations of foreign matter, or thelike.

While one illustrative embodiment of the invention has been described indetail, it is not my intention to limit its scope to that embodiment orotherwise than by the terms of the appended claims.

Having now described my invention, what I claim as new and desire tosecure by Letters Patent, is:

1. In a fluid pressure brake, in combination, a brake pipe, and anemergency valve device comprising a piston subject to the opposingpressures of the brake pipe and a chamber normally charged with fluidunder pressure, and valve means operative by said piston upon areduction in brake pipe pressure at a service rate for venting fluidunder pressure from said chamber at a service rate and operative by saidpiston upon a reduction in brake pipe pressure at an emergency rate foreffecting an emergency application of the brakes, and a volume reservoirnormally charged with fluid under pressure and connected to said chamberthrough a restricted port adapted at all times to limit the rate atwhich the pressure in said chamber is maintained by flow from saidreservoir to said chamber.

2. In a fluid pressure brake, in combination, a brake pipe, and anemergency valve device comprising a piston subject to the opposingpressures of the brake pipe and a chamber normally charged with fluidunder pressure, and valve means operative by said piston upon areduction in brake pipe pressure at a service rate for venting fluidunder pressure from said chamber at a service rate and operative by saidpiston upon a reduction in brake pipe pressure at an emergency rate foreffecting an emergency application of the brakes, and a volume reservoirnormally charged with fluid under pressure and connected to said chamberthrough a port of such size that sudden movement of said piston upon areduction in brake pipe pressure will reduce the pressure in saidchamber to a degree below that in said reservoir.

3. In a fluid pressure brake, in combination, a brake pipe, and anemergency valve device comprising a piston subject to the opposingpressures of the brake pipe and a chamber normally charged with fluidunder pressure, and valve means operative by said piston upon areduction in brake pipe pressure at a service rate for venting fluidunder pressure from. said'chamber at a service rate and operative bysaid piston upon a reduction in brake pipe pressure at an emergency ratefor effecting an emergency application of the brakes, and a volumereservoir normally charged with fluid under pressure and connected tosaid chamber through a port of such size that the increase in volume ofsaid chamber upon sudden movement of said piston will reduce thepressure in said chamber to substantially the pressure in the brake pipebefore said piston moves sufficiently to operate said valve means toeffect an emergency application of the brakes upon a service rate ofreduction in brake pipe pressure.

4. In a fluid pressure brake, in combination, a brake pipe, and anemergency valve device comprising a piston subject to the opposingpressures of the brake pipe and a chamber normally charged with fluidunder pressure, and valve means operative by said piston upon areduction in brake pipe pressure at a service rate for venting fluidunder pressure from said chamber at a service rate and operative by saidpiston upon a reduction in brake pipe pressure at an emergency rate foreffecting an emergency application of the brakes, and a volume reservoirnormally charged with fluid under pressure and connected to said chamberthrough a port of such size as will restrict the flow of fluid underpressure from said reservoir to said chamber upon sudden movement ofsaid piston whereby the pressure in said chamber will be reduced tosubstantially that in said brake pipe before said piston operates saidvalve means to effect an emergency application of the brakes, if upon aservice rate of reduction in brake pipe pressure said piston does notpromptly respond to a service rate of reduction in brake pipe pressure.

5. In a fluid pressure brake, in combination, a brake pipe, and anemergency valve device comprising a piston subject to the opposingpressures of the brake pipe and a chamber normally charged with fluidunder pressure, and valve means operative by said piston upon areduction in brake pipe pressure at a service rate for venting fluidunder pressure from said chamber at a service rate and operative by saidpiston upon a reduction in brake pipe pressure at an emergency rate foreffecting an emergency application of the brakes, said chamber being ofrelatively small volume whereby movement of said piston upon a reductionin brake pipe pressure will effect a substantial increase in the volumeof said chamber, and a reservoir of relatively large volume normallycharged with fluid under pressure and connected to said chamber througha port of such size that the pressure in said reservoir will notmaintain the pressure in said chamber upon sudden movement of saidpiston upon a reduction in brake pipe pressure.

6. In a fluid pressure brake, in combination, a brake pipe, and anemergency valve device comprising a piston subject to the opposingpressures of the brake pipe and a chamber normally charged with fluidunder pressure, and valve means operative by said piston upon areduction in brake pipe pressure at a service rate for venting fluidunder pressure from said chamber at a service rate and operative by saidpiston upon a reduction in brake pipe pressure at an emerency rate foreffecting an emergency application of the brakes, and a volume reservoirnormally charged with fluid under pressure and connected to said chamberthrough a port of such size that suddent movement of said piston willreduce the pressure in said chamber to substantially that in said brakepipe before said piston operates said valve means to effect an emergencyapplication of the brakes upon a service rate of reduction in brake pipepressure.

7. In a fluid pressure brake, in combination, a brake pipe, and anemergency valve device comprising a piston subject to the opposingpressures of said brake pipe and a chamber normally! charged with fluidunder pressure, a volume reservoir connected to said chamber andnormally charged with fluid under pressure, and valve means movable bysaid piston upon a reduction in brake pipe pressure at a service rate toa service position for establishing a communication through which thepressure of fluid in said chamber and reservoir is adapted to reduce ata service rate and movable past service position to an emergencyposition upon an emergency rate of reduction in brake pipe pressure foreffecting an emergency application of the brakes, a retriction in theconnection between said reservoir and chamber for limiting the rate offlow of fluid under pressure from said reservoir into said chamber uponmovement of said piston whereby, if the movement of said piston issudden upon a service rate of reduction in brake pipe pressure, theincrease in volume of said chamber due to .such movement will reduce thepressure in said chamber sufficiently to stop said piston and therebysaid valve means before reaching emergency position.

8. In a fluid pressure brake, in combination, a brake pipe, and anemergency valve device comprising a piston subject to the opposingpressures of said brake pipe and a chamber normally charged with fluidunder pressure, a volume reservoir connected to said chamber andnormally charged with fluid under pressure, and valve means movable bysaid piston upon a reduction in brake pipe pressure at a service rate toa service position for establishing a communication through which thepressure of fluid in said chamber and reservoir is adapted to reduce ata service rate and movable past service position to an emergencyposition upon an emergency rate of reduction in brake pipe pressure foreffecting an emergency application of the brakes, a restriction in theconnection between said reservoir and chamber for limiting the rate offlow of fluid under pressure from said reservoir into said chamber uponmovement of said piston whereby, if the movement of said piston issudden upon a service rate of reduction in brake pipe pressure,

the increase in volume of said chamber due to such movement will reducethe pressure in said chamber sufliciently to stop said piston andthereby said valve means in substantially service position in which saidcommunication is opened and the venting of fluid under pressure fromSaid chamber at a service rate will prevent further movement of suchpiston and valve means upon a service rate of reduction in brake pipepressure.

9. In a fluid pressure brake, in combination, a brake pipe, and anemergency valve device comprising a piston subject to the opposingpressures of said brake pipe and a chamber normally charged with fluidunder pressure, a volume reservoir connected to said chamber andnormally charged with fluid under pressure, and valve means movable bysaid piston upon a reduction in brake pipe pressure at a service rate toa service position for establishing a communication through which thepressure of fluid in said chamber and reservoir is adapted to reduce ata service rate and movable past service position to an emergencyposition upon an emergency rate of reduction in brake pipe pressure foreffecting an emergency application of the brakes, a spring operative tooppose movement of said piston and valve means past service position toemergency position, a restriction in the connection between saidreservoir and chamber operative upon sudden movement of said piston topermit the displacement volume of said piston toreduce the pressure insaid chamber sufficiently that said spring will prevent movement of saidpiston and valve means past the service position upon a service rate ofreduction in brake pipe pressure.

10. In a fluid pressure brake, in combination, a. brake pipe, anemergency valve device comprising a piston subject to the opposingpressures of said brake pipe and a valve chamber communicating with aquick action chamber, said valve and quick action chambers beingnormally charged with fluid under pressure, and valve means movable by acertain difierential established between the pressures in said brakepipe and valve chamber upon a service rate of reduction in brake pipepressure to a service position for effecting a service rate of reductionin pressure in said chambers and movable by a greater difierentialestablished upon an emergency rate of reduction in brake pipe pressureto an emergency position for efiecting an emergency application of thebrakes, and means for restricting the flow of fluid under pressure fromsaid quick action chamber to said valve chamber for preventingmaintenance of the pressure in said valve chamber upon sudden movementof said piston upon a reduction in brake pipe pressure whereby, if upona service rate of reduction in brake pipe pressure, a differential ofpressures as great as said greater difierential is obtained on saidpiston before said piston starts moving, the movement of said pistonwill reduce the differential to substantially said certain differentialbefore said piston moves said valve means past service position.

11. In a fluid pressure brake, in combination, a brake pipe, anemergency valve device comprising a piston subject to the opposingpressures of said brake pipe and a valve chamber communieating with aquick action chamber, said valve and quick action chambers beingnormally charged with fluid under pressure, and valve means movable by acertain differential established between the pressures in said brakepipe and valve chamber upon a service rate of reduction in brake pipepressure to a service position for effecting a service rate of reductionin pressure in said chambers and movable by a greater differentialestablished upon an emergency rate of reduction in brake pipe pressureto an emergency position for effecting an emergency application of thebrakes, spring means for opposing operation of said piston to move saidvalve means past service to emergency position upon a service rate ofreduction in brake pipe pressure, and means for restricting flow offluid under pressure from said quick action chamber to said valvechamber upon sudden movement of said piston, whereby, if upon a servicerate of reduction in brake pipe pressure a differential of pressures asgreat as said greater differential is obtained on said piston beforesaid piston starts moving, movement of said piston will reduce thepressure in said valve chamber and thereby the differential of pressureson said piston to a degree suificient that the pressure of said springwill prevent movement of said piston past service position.

12. In a fluid pressure brake, in combination, a brake pipe, anemergency valve device comprising a piston subject to the opposingpressures of said brake pipe and a valve chamber communicating with aquick action, chamber, said valve and quick action chambers beingnormally charged with fluid under pressure, and valve means movable by acertain differential established between the pressures in said brakepipe and valve chamber upon a service rate of reduction in brake pipepressure to a service position for eiiecting a service rate of reductionin pressure in said chambers and movable by a greater difi'erentialestablished upon an emergency rate of reduction in brake pipe pressureto an emergency position for effecting an emergency application of thebrakes, spring means for opposing operation of said piston to move saidvalve means past service to emergency position upon a service rate ofreduction in ,brake pipe pressure, and means for restricting flow offluid under pressure from said quick action chamber to said valvechamber upon sudden movement of said piston, whereby, if upon a servicerate of reduction in brake pipe pressure a differential of pressures asgreat as said greater diiferential is obtained on said piston beforesaid piston starts moving, movement of said piston will reduce thepressure in said valve chamber and thereby the differential of pressureson said piston to a degree sufiicient that the pressure of said springwill prevent movement of said piston past service position in which theventing of fluid under pressure from said chambers at a service ratewill prevent obtaining sufiicient differential of pressures on saidpiston to overcome said spring as the reductiotn in brake pipe pressurecontinues at a service ra e.

EVERETT P. SEXTON.

